Preparation And Characterization Of PVDF/ZIF-L Mixed Ultrafiltration Membrane

Ultrafiltration (UF) is a common process of water treatment, whose core component is UF membrane (UFM). UFM has been widely used during last few decades on account of its energy conservation, high efficiency and environment protection. UFMs are currently made of hydrophobic polymers, which are apt to membrane fouling, ending up with short service life and high expense, hence research of membrane hydrophilic modification is significant. At the present stage, mixed membrane is aimed to be prepared by blending hydrophilic materials including modified carbon nanotube (CNT) and metallic oxide with polymers, but research on metal-organic frameworks (MOFs) is few in UF field. In this article, ZIF-L, a novel type of MOFs with special structure and properties, was used to manufacture mixed UFM of good anti-fouling capacity and water treatment ability.First of all, membrane preparation condition was investigated according to basic performance of membranes. UFMs were prepared via nonsolvent-induced phase separation (NIPS) method of polyester non-woven fabrics with 140 ?m casting solution scraped on surface. The result of test of casting solution viscosity, pure water flux and molecules rejection shows that membrane with 18% PVDF load (P18) is appropriate to the foundation of modified UFM due to its moderate viscosity and acceptable withholding capacity.Next effect of varity and amount of alcohol additive to membrane performance, such as casting solution viscosity, pore size and water treatment properties, was examined. Results indicate that the addition of alcohols with single hydroxyl contributed to lower viscosity and smaller pore size. UFM with 4 wt.% ethanol (E4) exhibited the optimum data of 275 LMH pure water flux,98% bull serum albumin (BSA) and 97% ovalbumin (OVA) rejection.Finally performance of ZIF-L/PVDF mixed UFM was investigated. Preparation condition was determined by changing concentration and proportion of reactants, temperature and environment of reaction. Then the variation of viscosity, pore size and water treatment performance were inspected by altering load of ZIF-L. The results prove that membrane with ZIF-L/PVDF/ethanol load at 1.75/16.25/4 wt.%(Z175) shows the highest rejection of BSA (100%), OVA (100%), PEG35k (100%), PEG20k (100%), PEG 10k (99.6%), PEG6k (96.3%), and its pure water flux was 647 LMH,10 times of P18. Water contact angle, protracted pollution and atomic force microscope (AFM) tests shows that ZIF-L load debases the contact angle from 84° to 55°, flux recovery of Z175 approaches to 100%, surface roughness of Z175 decrease about 50% contrast with E4.